1. Field of the Invention
The present invention relates to a magnetic field generator for a magnetic force microscope, which measures magnetic force.
2. Description of the Related Art
In recent years, magnetic force microscopes, which enable the measurement of magnetic storage media magnetized in a very dense state and magnetization patterns of magnetic samples, have come into practical use (for example, see the following document; “The Digital Instruments Dimension 3100 Scanning Probe Microscope (SPM)” Retrieved Sep. 17, 2004, from http://www.veeco.com/html/datasheet—d3100.asp). The magnetic force microscope is one type of scanning force microscope, which makes non-contact measurements of a physical quantity. By bringing its cantilever, comprising a probe unit consisting of ferromagnetic material and a lever unit, into close proximity with the sample the magnetic force microscope measures the magnetic force generated between the surface of an object to be measured and the probe unit.
When scanned in the non-contact state by slightly separating the probe from the surface of the object to be measured, a magnetic force is generated between the object and the probe, and flexure is generated in the lever unit, which holds the probe. The magnetic field distribution can be measured by detecting the flexure using an optical lever method and by mapping the measured magnetic force in every position.
Cantilever probes for the atomic force microscope, which form the prototype of the magnetic force microscope, have individual variations in characteristics, and therefore sensitivity calibration of the probe is required before measurement. A common method of calibration is to determine the frequency characteristics of a probe by oscillating the probe by mechanical means so that the optimal oscillation amplitude in response to both the oscillation intensity and frequency can be determined.
Magnetic force microscopes also have individual variations in the magnetic characteristics of the cantilever probe, however means for calibrating this variation are not in practical use. The present situation, therefore, is that it is ultimately the frequency characteristic calibration method, of the same kind as that of the atomic force microscope that is used in the magnetic force microscope, and therefore individual variations in the magnetic characteristics of the probes cannot be calibrated.
In light of such a situation, a calibration method of measuring the oscillation frequency fluctuation by applying a direct-current magnetic field to a probe in a state of mechanical oscillation has been proposed (Japanese unexamined patent publication bulletin No. 07-072229, for example).
A magnetic recording head measurement device, which measures the magnetic force of the object to be measured using the magnetic force microscope, by generating a high-frequency magnetic field in the recording head is also widely known (Japanese unexamined patent publication bulletin No. 2001-266317, for example).
As explained above, cantilever probes for magnetic force microscopes have individual characteristics such as variations in the film thickness of the magnetic material used for the probe and probe tip shape. Such a situation causes variations in the measured distance as well as variations in the detected magnetic field intensity however the methods currently in practice cannot be used to compensate for these variations. Even the method of mechanically oscillating the probe cannot be used to correct the measurement distance.